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It is known that leafy vegetables including spinach (Spinacea oleracea L.) contain relatively high amount of water, therefore, their water requirement during the life cycle is comparatively more than the other vegetables. In addition, there is an association between osmoprotection and antioxidants with reference to drought stress tolerance. Keeping in mind these facts, the present study was conducted to assess the changes in plant growth, osmoprotectants, chlorophyll pigments and activities/levels of antioxidative system in spinach (Spinacea oleracea L.) grown under varying water deficit regimes with 40%, 60%, 80% and 100% field capacity (FC). Imposition of varying water regimes significantly decreased shoot and root fresh and dry weights, shoot plus root lengths, and chlorophyll b contents of spinach plants. Increase in proline, glycinebetaine (GB), total phenolics, ascorbic acid and malondialdehyde (MDA) contents as well as the activities of antioxidant enzymes including superoxide dismutase, peroxidase and catalase were observed in the spinach plants particularly at 40% FC. The most effective level of water stress for elevating the proline, GB and antioxidant levels/ activities was observed at 40% FC followed by 60% FC. Hence, the results of this study suggested that upregulation of antioxidants and osmoprotectants is positively associated with the drought tolerance of spinach which depends on the severity of water stress level. These results can be used to narrow the gap between selection of plant species and requirement of irrigated water for the crops grown on dry land areas. ABSTRAKAdalah diketahui bahawa sayur-sayuran berdaun termasuk bayam (Spinacea oleracea L.) mengandungi jumlah air yang agak tinggi, oleh itu, mereka memerlukan lebih air sepanjang kitaran hidup berbanding sayur-sayuran lain. Di samping itu, terdapat hubungan antara osmoperlindungan dan antioksidan berkaitan toleransi tekanan kemarau. Dengan mengambil kira fakta tersebut, kajian ini dijalankan untuk menilai perubahan dalam pertumbuhan tanaman, osmoperlindungan, pigmen klorofil serta aktiviti/tahap sistem antioksidatif pada bayam (Spinacea oleracea L.) yang ditanam di bawah rejim defisit air berbeza dengan 40%, 60%, 80% dan 100% kapasiti lapangan (FC). Pengenaan rejim air yang berbeza dengan ketara mengurangkan berat segar dan kering pucuk dan akar, panjang pucuk dan akar serta kandungan klorofil b pada pokok bayam. Pertambahan kandungan prolin, glisinbetain (GB), jumlah fenolik, asid askorbik dan malondialdehid (MDA) serta aktiviti enzim antioksida termasuk superoksida dismutase, peroksidase dan katalase telah diperhatikan pada tanaman bayam terutamanya pada 40% FC. Tahap tekanan air paling berkesan untuk meningkatkan tahap/aktiviti proline, GB dan antioksidan diperhatikan pada 40% FC diikuti 60% FC. Oleh itu, keputusan kajian ini mencadangkan pengawalaturan atas antioksidan dan osmoperlindungan dikaitkan secara positif dengan toleransi kemarau oleh bayam yang bergantung pada keterukan aras tekanan air. Keputusan ini boleh digunakan unt...

Thiamin, an important member of the vitamin B family, is believed to play a significant role in mitigating environmental stresses including drought stress. In turnip, drought stress causes a reduced growth, biomass yield, pigment content, total phenolics and ascorbic acid (AsA), particularly at 50% field capacity (F.C.) in the two cultivars (cv) studied. However, a significant enhancement was observed in the contents of leaf proline, glycinebetaine (GB), malondialdehyde (MDA), hydrogen peroxide (H 2 O 2 ) and the activities of catalase (CAT) and superoxide dismutase (SOD) as well as root proline, GB, total phenolics, AsA, H 2 O 2 , MDA and the activities of peroxidase (POD) and SOD. However, foliar-applied thiamin significantly improved (particularly 100 mM) all the growth attributes, photosynthetic pigments, leaf and root osmoprotectants (GB and proline), AsA, total phenolics and the activities of enzymatic antioxidants such as SOD and POD as well as root CAT in both turnip cultivars under drought stress conditions. Foliar application of thiamin was effective in decreasing the leaf and root H 2 O 2 and MDA content in both cultivars particularly at 50% F.C. Thiamin-induced growth of both turnip cultivars, particularly of cv. Purple Top, was found to be associated with increased photosynthetic pigments, proline and GB contents and antioxidant capacity, but reduced levels of reactive oxygen species (ROS) under water deficit conditions. So, it is suggested that exogenous application of thiamin can be effective in improving drought tolerance of plants.

Thiamin is a crucial vitamin with a vast variety of anti-oxidative and physiological roles in plants subjected to abiotic stresses. We examined the efficiency of foliar-applied thiamin (50 and 100 mM) on growth, yield quality and key-biochemical characteristics of two cultivars (FD1 and FD3) of cauliflower (Brassica oleracea L.) under water-deficit stress. Water stress at the rate of 50% field capacity (F.C.) markedly decreased the plant biomass, leaf total phenolics and ascorbic acid (AsA) contents. In contrast, drought-induced increase was noted in the leaf [hydrogen peroxide (H2O2), AsA, proline, malondialdehyde (MDA), glycinebetaine (GB), total soluble proteins and oxidative defense system in terms of high activities of peroxidase (POD), and catalase (CAT) enzymes] and the inflorescence (total phenolics, proline, GB, MDA, H2O2, and activities of SOD and CAT enzymes) characteristics of cauliflower. However, foliar-applied thiamin significantly improved growth and physio-biochemical attributes except leaf and inflorescence MDA and H2O2 contents of both cauliflower cultivars under water stress. Overall, application of thiamin enhanced the plant growth may be associated with suppressed reactive oxygen species (ROS) and upregulated antioxidants defense system of cauliflower.

Plants face assorted of abiotic stresses such as, salinity, drought and heavy metals which produce ROS, and finally inhibit normal growth plant production. To stop cellular destruction due to oxidative stress, these abiotic stresses increase complex reactions in plants to avoid damage and boost their sustainability under severe stress situations. Plants produce several organic solutes known as osmoprotectant such as, polyamines, sugars, proline and glycinebetaine (GB), to adjust the cellular mechanism and stable the membrane structure and proteins towards environmental stress. As well, they also defend the plant cells from oxidative stress by stopping the accumulation of damaging effect of ROS. In this review, we have deliberated the mechanisms of organic solutes as well as several functions in plants under abiotic stress situations. The organic solutes that are also known as osmolytes/osmoprotectants comprise soluble sugars, proline and glycinebetaine.